1. Field of the Invention
The invention relates to an image projection system, and more particularly, to an image projection system that is installed with an_invisible-light reflector according to a predetermined angle and a predetermined position for heat dissipation.
2. Description of the Prior Art
With the promotion of the electro-optic techniques, projecting devices are widely used in various applications. Nowadays, the projecting devices include CRT projectors, LCD projectors, and DMD-based DLP5. In addition, LCOS projectors are expected future stars in the projecting industry. The basic operating principle of various projecting devices is the same: utilizing a high-luminance light source to emit a light beam that then will be passed though some specific optical image modules, such as optical filter, to be projected on a screen with informative content. Generally, the optical power of the high-luminance light source will crucially affect the projecting performance of the projecting device. In brief, higher optical power of the high-luminance light source will lead to a better projecting performance of the projecting device.
Please refer to FIG. 1, which is an image projection system 10 according to the prior art. The image projection system 10 includes a light source 12, a reflective housing 14, an image module 16, and an optical component 18. The image projection system 10 may further comprise a glass 20 as an R-G-B color wheel or as a protection glass. The light source 12 is used to generate a light beam, and the reflective housing 14 can be an elliptic reflective housing. The light source 12 is installed at a focal point of the elliptic reflective housing 14, and the reflective housing 14 forms an accommodating space and includes an opening. The light source 12 is installed inside the accommodating space, so that the light beam generated by the light source 12 substantially propagates along an optical path through the opening away from the accommodating space after being reflected by the elliptic reflective housing 14. The image module 16 includes a plurality of controllable reflectors for generating a projecting beam containing an optical image. The optical component 18, which comprises prisms and lens, is used to focus and output the projecting beam containing the optical image.
Design of the high-luminance light source will crucially affect the projecting performance of the projecting device. In U.S. Pat. No. 6,281,620. “Lamp with IR reflectivity”, Yeh et al. disclose a bulb that can be used to reflect infrared rays, and Yeh et al. also teach a method for increasing the luminance efficiency by focusing the reflected infrared rays on the lamp wick. In U.S. Pat. No. 6,398,367, “Light source device and projector using the light source device”, Watanabe et al. teach that the light source 12 and the reflective housing 14 shown in FIG. 1 can be detachably integrated. In addition, Watanabe et al. also provide a protection for the image projection system 10 with a transparent front glass at the opening of the reflective housing 14. Moreover, in U.S. Pat. No. 6,185,047, “Image projection system packaged to operate lying flat with a very low profile”, Peterson et al. further install a color wheel 20 coated with an ultraviolet-rays-proof coating in the system shown in FIG. 1 for filtering out the ultraviolet rays so that the ultraviolet rays will not damage the image module 16 and optical component 18 inside the image projection system 10. Designs similar to the above-mentioned structure can also be found in U.S. Pat. No. 6,299,310, “Luminous intensity detection and control system for slit lamps and slit lamp projections”.
The above-mentioned prior-art techniques, which make use of a higher optical power of the high-luminance light source to improve the projecting performance of the projecting device, are no longer useful. First, when designers raise the optical power of the light source from about 100 W to higher than 200 W or 400 W. The heat dissipation becomes a problem difficult to handle in the image projection system 10 as shown in FIG. 1. The traditional design for heat dissipation including installing at least a fan in the image projection system cannot dissipate the infrared-ray heat generated from the light source. In addition, destructive infrared-ray heat combined with ultraviolet rays generated from the extremely-high-luminance light source may seriously damage all components of the image projection system 10 shown in FIG. 1, including the light source 12, the reflective housing 14, and so on. Therefore, the image projection system installed with the extremely-high-luminance light source should be equipped with an effective heat-dissipation design.